[Cryptech Tech] Suggested changes to TRNG

[Joachim Strömbergson]

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Aloha!

Benedikt Stockebrand wrote:
> Anyway, what I've done with the ARRGH firmware was to wait until
> I've seen all 256 byte values from the source and only then start
> passing random data out.
> 
> This is probably a bit over the top, but it's still reasonably fast
> to start up.  It's reasonably easy to do in an MCU; don't know about
> FPGAs, though.

Takes a 256 bit wide register and a big honking 256-1 AND gate. Done. ;-)


> Using a fixed interval is a bad idea because a fixed interval won't 
> adapt to tolerances of the components etc.

That is true. One would however also need to add a timer to be able to
say that longer then XYZ ms before seeing all 256 bit values and the
entropy source is probably dead. Otherwise you could wait indefinitely.

Also, the warmup is just to give the noise sources time to properly
start, not ensure that they operate correctly. That is the
responsibility of the the startup test and online monitors. So I don't
think we should spend to much resources on the warmup function. Your
solution would require more registers, but not much else.

Good idea, thanks!

- -- 
Med vänlig hälsning, Yours

Joachim Strömbergson - Alltid i harmonisk svängning.
========================================================================
 Joachim Strömbergson          Secworks AB          joachim at secworks.se
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